Compressive stress induced the up-regulation of M-CSF, RANKL, TNF-α expression and the down-regulation of OPG expression in PDL cells via the integrin-FAK pathway.

OBJECTIVES

This study was performed to elucidate the involvement of integrin-FAK (focal adhesion kinase) pathway in compressive stress-induced mRNA expression of macrophage colony stimulating factor (M-CSF), tumour necrosis factor (TNF)-α, receptor activator of nuclear factor κB (RANKL) and osteoprotegerin (OPG) and to further confirm the role of the integrin-FAK complex as a mechanoreceptor in PDL cells.

DESIGN

Periodontal ligament (PDL) cells were obtained from patients having healthy first premolars extracted for orthodontic purposes. Cultured PDL cells were divided into three groups: the control group in which compressive stress was administered; the negative control group in which mechanical stress was administered after transfection of negative control siRNA; and FAK knockdown group in which mechanical stress was administered after FAK siRNA treatment. Compressive stress (2g/cm(2)) was for various time durations (0.5, 2, 6, 24, 48h). Total RNA was collected after the experiment and real-time PCR analysis was performed to determine the mRNA expression levels of M-CSF, TNF-α, RANKL and OPG. Also the supernatant was analysed with ELISA to detect the corresponding cytokine concentrations.

RESULTS

The cells of the control group and the negative control group expressed higher mRNA levels of M-CSF, TNF-α, and RANKL but a lower mRNA level of OPG compared to those of baseline. FAK knockdown cells showed lower mRNA expression levels of M-CSF, TNF-α, and RANKL but a higher mRNA expression level of OPG than that in the control. The OPG mRNA expression level in FAK knockdown cells was even higher than that of baseline. ELISA results showed similar pattern of cytokine concentration changes.

CONCLUSIONS

Results of this study indicate that the integrin-FAK pathway regulates compressive stress-induced expression of M-CSF, TNF-α, RANKL and OPG and suggests that the integrin-FAK complex acts as a mechanoreceptor in PDL cells.